Array[`replace`/`replaceAll`/`groupBy`]

polyfill.js

const defineArr = (prop, value) => {
    if (!Array.prototype.hasOwnProperty(prop)) {
        Object.defineProperty(Array.prototype, prop, {
            value
        });
    }
};

defineArr('groupBy', function value(fn) { return this.reduce((p, c, i) => {
    const k = fn(c, i, p);
    return { ...p, [k]: [...(p[k] || []), c] };
}, {}) });

defineArr('replace', function value(filter, value) {
    const cpy = [...this];
    cpy[cpy.findIndex(filter)] = value;
    return cpy;
});

defineArr('replaceAll', function value(filter, value) {
    return this.map((val, indx, arr) => (filter(val, indx, arr) ? value : val));
});

polyfill.ts

/*
https://www.typescriptlang.org/play?target=6#code/C4TwDgpgBAShYBsCGBjCAnAYgVwHYuAEsB7XAHgBUA+KAXigApgALQgZwC4oKBtAXQA0UAGaEEwDFwYA3JAmwQuFIYVwATCAA8uubAFsARhiFJ06JCCX8AlHRp4A1rmIB3XENnzF3W7Rq8+AChAjRRkdGhVCXRhVGgAQTMLShoAb0CoTKgIxDiuOFy0LDwCEnJqAG4MrJzkNHiEBHz4OowcfCJSFKqAX2DE8xAAOjB0YmBx8Agh2rioAH55+mESztxGFnYhUXFjKE8FW3SsqBRSNmBTsBA6KB4hh822PiqTlGued+HRdQBJdS0DB20WsfFuBwgrxqEGA2HQ6y+vSqgQGFhGYwmoEgMxacQaCAWSxEqzKG1YbG2YmiHjkhygx2hsPhUCeQz0SDADBkchU6k0JjMvhowIw3IQvLU-KgpnQtnm+1p0C4nmsgR6yIA9AAqFFJYajcaTbGzeqNW4rDqklIMaqZJ5WQS2kRUySMCFKCVaHT6IzoAWDB1CqCOZxuARO93cQJHJ0RJnrVnszliiVSmVBkXoFNQVSS-1yhVeKDKuSq9WBLUa4KBM64C5QL1QVEgMhIXAgGj0HgARiEAGYhAA2IQAFhewVr9YQxAA5rcGA8hqYZ5xpe2g5PiAhptOZwxl2w2RyuUguG2QEGAOQAHVwl6gAGooAApADKAHkAHJDC7oVQzwhhBAfdrGsIYJlfYA-1wPdQOCXcGC0IRL2gGgAFY7EvIQtBxQoIEQuwGygdDkJNCA1EvOCEKQqAUKgABSKAACYoAAQnoAAGTDsM0XDWnxAi-CIximNI3E0AouDgg1DVuGIKBt1MdY9GICJpQMYhsEuFhoGQGDsCQGcICEMJCBQBx1OIaRInWAAiABRTQkD0RAIDYWyoFUqBbIAdWYJBgEvNgoE-CAXFsoZAhkqB3x09AXHYYyoCMy4LlMCQ1CgAwbgiFTpH-FlmDc6Azj0PQIFwYBgrbTKdKgFxVIQTL2CgEBNPQKBchAGcxjwNRIqAA
*/

// TypeScript part
type ReplacerFunction<T> = (
    this: T[],
    filter: (value: T, index: number, array: T[]) => unknown,
    value: T
) => T[];

declare interface Array<T> {
    replace: ReplacerFunction<T>;
    replaceAll: ReplacerFunction<T>;
}

// JavaScript part
Array.prototype.replace ??= function (this, filter, value) {
    const cpy = [...this];
    cpy[cpy.findIndex(filter)] = value;
    return cpy;
};

Array.prototype.replaceAll ??= function (this, filter, value) {
    return this.map((val, indx, arr) => (filter(val, indx, arr) ? value : val));
};